1. Field of the Invention
The present invention relates to a terahertz wave transmission and reception (Tx/Rx) module package and method of manufacturing the same, and more particularly to a technique for simply aligning a silicon ball lens, a photoconductive antenna and a focusing lens to implement a complete and separate terahertz wave Tx/Rx module package.
2. Discussion of Related Art
Terahertz waves are electromagnetic waves ranging from 100 GHz to 10 THz between infrared rays and microwaves. Lately, terahertz waves have been approved as future electric wave resources due to the development of high technology. Accordingly, terahertz waves are attracting attention all over the world, and becoming more important in various fields through fusion with information technology (IT), bio technology (BT), etc.
In particular, terahertz waves transmit through various materials like electric waves while traveling straight like visible rays, and thus can be used in basic science, such as physics, chemistry, biology and medical science. Since terahertz waves can be used to detect counterfeit bills, drugs, explosives, biochemical weapons, etc., and to non-destructively examine industrial structures, they are also expected to be extensively used in fields of general industry, national defense, security, etc. Furthermore, terahertz technology is expected to be extensively used for wireless communication at 40 Gb/s or higher, high-speed data processing and inter-satellite communication in the IT field.
Terahertz waves can be classified into continuous waves and pulse waves. In general, the pulse terahertz waves are generated by radiating a femtosecond (10−15 second) laser onto a special semiconductor or optical crystal. This will be described below in further detail.
FIG. 1 illustrates a method of generating a pulse terahertz wave by radiating a femtosecond laser onto a photoconductive antenna.
Referring to FIG. 1, a photoconductive antenna 100 includes a photoconductive thin film 120 formed on a semi-insulating GaAs substrate 110, and parallel metal transmission lines (also functioning as electrodes) 130 formed on the photoconductive thin film 120 and having middle protrusions. Here, the middle protrusions of the parallel metal transmission lines 130 function as a small dipole antenna.
When excitation is intermittently performed using laser pulse light fs having a time width of 100 femtoseconds or less with a bias voltage Vb applied to the parallel metal transmission lines 130, carriers (electrons and holes) are generated by light absorption, and current instantly flows through the parallel metal transmission lines 130. As a result, a terahertz wave (dipole radiation) proportional to a value obtained by differentiating the current with respect to time is generated.
The generated terahertz wave is intensely radiated from the surface of the substrate 110 having high permittivity, and the pulse width of the radiated terahertz wave is 1 ps or less. When light excitation is performed using a general-use laser pulse of 30 fs or more, a spectrum obtained by Fourier transform has a broad frequency band from 0 to several terahertz.
In order to radiate a terahertz wave from a substrate surface as mentioned above, a femtosecond laser pulse should be focused onto the photoconductive antenna 100 through a focusing lens and transformed into the frequency domain, and then focused again onto a predetermined region through a silicon ball lens.
According to conventional art, all devices such as a focusing lens, a photoconductive antenna, and a silicon ball lens are mounted and aligned on an optical table to manufacture a terahertz wave Tx/Rx module. Thus, to precisely bring the devices into surface contact with each other, a high precision alignment technique is necessary.
In particular, when a photoconductive antenna and a hemispherical silicon ball lens are brought into surface contact with each other, surfaces of the photoconductive antenna and the silicon ball lens may be scratched, an alignment error may occur, and an additional fixing means is needed to keep the photoconductive antenna and the silicon ball lens aligned.
Also, a wire should be directly connected with a photoconductive antenna using a conductive adhesive or indium bonding in order to test characteristics of a generated terahertz wave, and should be removed again using the conductive adhesive or indium bonding after the test is finished. Thus, it is very troublesome and difficult to test characteristics of the terahertz wave while keeping the photoconductive antenna and the silicon ball lens aligned as they are.
Furthermore, alignment of the focusing lens, the photoconductive antenna and the silicon ball lens may be easily disturbed during transportation and storage, and the devices may be easily damaged or polluted by surroundings.